refactor(G.3a): Place flips Idle before delegate; test mid-hold reset (#133)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/World/TeleportArrivalController.cs

@@ -97,7 +97,9 @@ public sealed class TeleportArrivalController
 
     private void Place(bool forced)
     {
-        _place(_destPos, _destCell, forced);
+        // Flip to Idle BEFORE invoking the placement delegate so the machine
+        // reflects "done holding" even if the delegate were to re-enter Tick.
         Phase = TeleportArrivalPhase.Idle;
+        _place(_destPos, _destCell, forced);
     }
 }

tests/AcDream.App.Tests/World/TeleportArrivalControllerTests.cs

@@ -120,4 +120,28 @@ public class TeleportArrivalControllerTests
         Assert.Equal(2, placed.Count);
         Assert.Equal(0x01250127u, placed[1].Cell);
     }
+
+    [Fact]
+    public void BeginArrival_DuringHold_ResetsTimeoutCounter()
+    {
+        var placed = new List<PlaceCall>();
+        var c = Make(ArrivalReadiness.NotReady, placed, maxHoldFrames: 3);
+
+        c.BeginArrival(new Vector3(1, 0, 0), 0x01250126u);
+        c.Tick(); // held=1
+        c.Tick(); // held=2 (one short of the timeout)
+
+        // Re-arm mid-hold with a fresh destination: the counter must restart.
+        c.BeginArrival(new Vector3(2, 0, 0), 0x01250199u);
+        c.Tick(); // held=1 again (NOT 3 -> no placement yet)
+        c.Tick(); // held=2
+        Assert.Empty(placed);
+        Assert.Equal(TeleportArrivalPhase.Holding, c.Phase);
+
+        c.Tick(); // held=3 -> timeout, forced place of the SECOND destination
+        var call = Assert.Single(placed);
+        Assert.True(call.Forced);
+        Assert.Equal(0x01250199u, call.Cell);
+        Assert.Equal(new Vector3(2, 0, 0), call.Pos);
+    }
 }